Clinical studies related to cardiac pacing have shown that an optimal atrioventricular pacing delay (e.g., AV delay or PV delay) and/or an optimal interventricular pacing delay (e.g., VV delay) can improve cardiac performance. However, such optimal delays depend on a variety of factors that may vary over time. Thus, what is “optimal” may vary over time. An optimization of AV/PV pacing delay and/or VV pacing delay may be performed at implantation and sometimes, a re-optimization may be performed during a follow-up consultation. While such optimizations are beneficial, the benefits may not last due to changes in various factors related to device and/or cardiac function.
The following patents and patent applications set forth various systems and methods for allowing a pacemaker, ICD, CRT or other cardiac rhythm management (CRM) device to determine and/or adjust AV/PV/VV pacing delays so as to help maintain the pacing delays at optimal values: U.S. patent application Ser. No. 10/703,070, filed Nov. 5, 2003, entitled “Methods for Ventricular Pacing”; U.S. patent application Ser. No. 10/974,123, filed Oct. 26, 2004; U.S. patent application Ser. No. 10/986,273, filed Nov. 10, 2004; U.S. patent application Ser. No. 10/980,140, filed Nov. 1, 2004; U.S. patent application Ser. No. 11/129,540, filed May 13, 2005; U.S. patent application Ser. No. 11/952,743, filed Dec. 7, 2007. See, also, U.S. patent application Ser. No. 12/328,605, filed Dec. 4, 2008, entitled “Systems and Methods for Controlling Ventricular Pacing in Patients with Long Intra-Atrial Conduction Delays”; U.S. patent application Ser. No. 12/132,563, filed Jun. 3, 2008, entitled “Systems and Methods for determining Intra-Atrial Conduction Delays using Multi-Pole Left Ventricular Pacing/Sensing Leads”; and U.S. patent application Ser. No. 12/639,881, filed Dec. 16, 2009, entitled “Systems and Methods for Determining Ventricular Pacing Sites for use with Multi-Pole Leads.” See, further, U.S. Pat. No. 7,248,925, to Bruhns et al., entitled “System and Method for Determining Optimal Atrioventricular Delay based on Intrinsic Conduction Delays.” At least some of the techniques are implemented within the QuickOpt™ systems of St. Jude Medical.
In particular, intracardiac electrogram (IEGM)-based techniques are set forth within at least some of these documents for exploiting various inter-atrial and interventricular conduction delays observed within the IEGM to determine preferred or optimal VV pacing delays for use in delivering CRT. Briefly, CRT seeks to normalize asynchronous cardiac electrical activation and resultant asynchronous contractions associated with congestive heart failure (CHF) by delivering synchronized pacing stimulus to both ventricles. The stimulus is synchronized so as to improve overall cardiac function. This may have the additional beneficial effect of reducing the susceptibility to life-threatening tachyarrhythmias.
IEGM-based methods for the optimization of VV delays are generally based on the hypothesis that minimizing electrical activation time in the left ventricle (LV) can lead to improved mechanical synchrony in many CRT patients. That is, pacing is directed toward reducing the width of ventricular depolarization events (QRS complexes.) However, in some patients, achieving a shorter paced QRS width (with biventricular pacing) does not result in significant improvement in mechanical synchrony due to functional blocks formed during biventricular pacing. This phenomenon appears to be specific to so-called CRT nonresponders. New methods for improving mechanical synchrony in this group of patients would be helpful in reducing the number of CRT nonresponders.
Accordingly, it would be desirable to provide improvements in the determination of preferred or optimal VV pacing delays for use with CRT and aspects of the present invention are directed to that general goal. In particular, it would be desirable to provide techniques for identifying optimal ventricular pacing locations/vectors and for setting optimal VV pacing delays so as to allow CRT to be delivered more effectively within patients otherwise considered to be CRT nonresponders.